This invention relates to a phase shifter and, more particularly, to a phase shifter available for a power amplifier, a balance-type modulator/demodulator and a mixer.
The main function of the phase shifter is an electric power distribution from an unbalanced signal and a balanced signal different in phase from the unbalanced signal at a predetermined angle such as 180 degrees without changing the amplitude. For this reason, the 180-degree phase shifter is called as a balanced-unbalanced converter or simply as balun.
A small wide-band balun is proposed by G. J. Laughlin in xe2x80x9cA New Impedance-Matched Wide-Band Balun and Magic Treexe2x80x9d, IEEE Trans. Microwave Theory Tech., vol. MTT-24, No. 3, March 1976, page 135 to page 141, and is illustrated in FIG. 1. The prior art balun has an input terminal 51 assigned to an unbalance signal and output terminals 52/53 assigned to balance signals.
The prior art balun includes an unbalanced transmission line 54, two balanced transmission lines 58/59, a coupled transmission line 55 with an open-end and coupled transmission lines 56/57 each having a grounded end E and an open end. The transmission line 54 and the transmission line 55 connected to the transmission line 54 are coupled through the transmission lines 56 and 57 to the transmission lines 58 and 59, respectively. The unbalanced signal is supplied to the input terminal 51, and is propagated through the abovedescribed transmission lines to the output terminals 52 and 53.
FIGS. 2A and 2B illustrate the arrangement and the structure of the prior art balun. The transmission lines 54, 55, 56, 57, 58 and 59 are patterned on a dielectric substrate 63, and the dielectric substrate 63 (see FIG. 2B) is 0.8 millimeter thick. The dielectric substrate 63 is formed of dielectric material, the dielectric constant of which is 2.2. The prior art balun is designed at 2.5 GHz, and introduces the phase difference of 180 degrees.
On the top surface of the dielectric substrate 63 are formed the transmission line 54 connected to the input terminal 51 to which the unbalanced signal is supplied, the open-ended transmission line 55 connected to the transmission line 54 and the transmission lines 58 and 59 respectively connected to the output terminals 52 and 53 from which the balanced signals are respectively output. The outlines of the transmission lines 54, 55, 58 and 59 and the input/output terminals 51, 52 and 53 are indicated by real lines in FIG. 2A. The other transmission lines 56 and 57 are patterned on the reverse surface of the dielectric substrate 63. The transmission lines 56 and 57 are open at one ends thereof, and are grounded through a box 60, as shown in FIG. 2A. The outlines of the transmission lines 56 and 57 are indicated by broken lines in FIG. 2A. The transmission line 56 is overlapped with the transmission lines 54 and 58 so as to be coupled through the dielectric substrate 63 with the transmission lines 54 and 58. On the other hand, the transmission line 57 is overlapped with the transmission lines 55 and 59 so as to be coupled through the dielectric substrate 63 with the transmission lines 55 and 59. The length of each transmission line is adjusted to a quarter wavelength of the signal at 2.5 GHz. In order to short-circuit one end of the transmission line 56 to one end of the transmission line 57, a cavity 64 is formed in the box, and the cavity 64 is 1.2 millimeter in depth, as shown in FIG. 2B.
FIG. 3A illustrates the transmission lines 54, 55, 58 and 59 patterned on the top surface of the dielectric substrate 63, and FIG. 3B illustrates the transmission lines 56 and 57 patterned on the reverse surface of the dielectric substrate 63. The periphery of the reverse surface is grounded, and is netted in FIG. 3B.
The prior art 180-degree phase shifter shown in FIGS. 2A and 2B is available for a power distribution/power composer of a power amplifier. In this instance, the designer encounters a problem in that he can not optimize the location of the input terminal 51 and the locations of the output terminals 52/53. In detail, the unbalanced signal input terminal 51 is coupled only through the transmission lines 56 and 57 with the balanced signal output terminals 52 and 53. This means that the unbalanced signal input terminal 51 and the balanced signal output terminals 52/53 set the limit on one another. The unbalanced signal is supplied from the input terminal 51 to the transmission line 54, and the transmission line 54 is coupled through the transmission line 56 serving as a ground electrode with the transmission line 58 from which the balanced signal is output. The open-ended transmission line 55 provides a quasi ground for the unbalanced signal, and is coupled through the transmission line 57 serving as the ground electrode with the transmission line 59 from which the balanced signal is output. Thus, the transmission line 54 on the top is to be overlapped with the transmission line 58 on the reverse surface, and the designer has to locate the transmission line 54 between broken lines A and B (see FIG. 2A). Thus, the prior art 180-degree phase shifter
The prior art 180-degree phase shifter is further available for a push-pull power amplifier shown in FIG. 4A. The prior-art push-pull power amplifier includes 180-degree phase shifters 73 and 74, two power transistors 75 and composite circuit components 76 and 77. The two power transistors 75 are located between the composite circuit components 76 and 77, and each of the composite circuit components 76 and 77 has a bias circuit and a transmission line. The two power transistors 75 are shown in FIG. 4B. Gate electrodes 75a are located on one side, and drain electrodes 75b are located on the other side. Returning to FIG. 4A, gate bias terminals 78 and 79 are connected through the composite circuit component 76 to the gate electrodes 75a (see FIG. 4B), and drain bias terminals 80 and 81 are connected through the composite circuit component 76 to the drain electrodes 75b (see FIG. 4B).
An input power signal is supplied from an input terminal 71 to the prior art 180-degree phase shifter 73, and the prior art 180-degree phase shifter separates the input power signal into two power signals. The power signals are 180 degrees different in phase from each other, and are supplied through the composite circuit component 76 to the power transistors, respectively. The power transistors 75 operate at the phase difference, i.e., 180 degrees, and carry out the power amplification. The power transistors 75 supply the amplified power signals through the composite circuit component 76 to the prior art 180-degree phase shifter 74, and the prior art 180-degree phase shifter 74 composes an output power signal. The output power signal is supplied to an output terminal 72.
The prior art push-pull power amplifier is available for a high-power power amplifier. FIG. 5 illustrates the prior art high-power power amplifier. Plural prior art push-pull power amplifiers 45 are connected in parallel between a power distributor 43 and a power composer 44, and an input terminal 1 and an output terminal 21 are connected to the power distributor 43 and the power combiner 44, respectively. The push-pull power amplifiers 45 are similar in circuit configuration to the prior art push-pull power amplifier shown in FIG. 4A, and the 180-degree phase shifters 73/74 are incorporated in each of the push-pull power amplifiers 45. The unbalanced signal terminals of the 180-degree phase shifters 73/74 are arranged to be opposite to each other from the aspect that the plural push-pull power amplifiers are combined. However, the unbalanced signal terminal is coupled through transmission lines with the associated balanced signal terminal, and the designer can not independently locate the unbalanced terminal and the balanced terminal. In this situation, when the designer intends to combine the prior art push-pull power amplifier with other devices or circuits, the designer needs to arrange signal lines to connect the unbalanced/balanced terminals to the other devices or the circuits, and the signal lines tend to be complicated. This results in increase of the circuit board and decrease of the efficiency of power composition.
It is therefore an important object of the present invention to provide a phase shifter, which has an input terminal and output terminals independently locatable.
It is also an important object of the present invention to provide a phase shifter, which makes a power amplifier compact and enhances characteristics of the power amplifier.
To accomplish the object, the present invention proposes to associate a balanced signal transmission line and an unbalanced signal transmission line with transmission lines independently.
In accordance with one aspect of the present invention, there is provided a phase shifter comprising a first signal transmission path connected to an input signal port, a second signal transmission path connected to an output signal port, a third signal transmission path capacitively coupled with the first signal transmission path and a fourth signal transmission path connected to the third signal transmission path, capacitively coupled with the second signal transmission path and cooperating with the third signal transmission path for introducing a predetermined phase difference between the first signal transmission and the second signal transmission path.